Fig. 5: The non-Hermitian Su-Schrieffer-Heeger model.
From: Activating non-Hermitian skin modes by parity-time symmetry breaking
a A sketch of the model of Eq. (11), with γ (g) the asymmetric hopping (gain/loss) parameter. b Typical spectra of Hg under periodic (gray) and open (other colors) boundary conditions (PBCs and OBCs). Under the OBCs, bulk states can be parity-time-symmetric (\({{{{{{{\mathcal{PT}}}}}}}}\) symmetric) and have real eigenenergies (black), but edge states are \({{{{{{{\mathcal{PT}}}}}}}}\)-broken and have imaginary eigenenergies ± ig (red and blue). Insets demonstrate the spatial distribution of corresponding eigenstates. c Typical PBC and OBC spectra of Hγ, with the same color marks as in b. The PBC spectrum in c is \({{{{{{{\mathcal{PT}}}}}}}}\)-broken and possesses a nontrivial spectral winding, leading to a boundary accumulation of all eigenstates (see insets). The OBC spectrum restores a non Bloch (or a generalized) \({{{{{{{\mathcal{PT}}}}}}}}\) symmetry and becomes purely real. Parameters are chosen to be u = 0.5, v = 1, and b g = 0.2, c γ = 0.2 for demonstration.
